1. Field of Invention
The invention relates to wireless communications, and more specifically to automatic gain control performed within a wireless communication device that adjusts gain independent of frame loading.
2. Related Art
Wireless communication devices, such as cellular telephones to provide an example, are becoming commonplace in both personal and commercial settings. The wireless communication devices provide users with access to all kinds of information. For example, a user can access the internet through an internet browser on the device, download miniature applications (e.g., “apps”) from a digital marketplace, send and receive emails, or make telephone calls using a voice over internet protocol (VoIP). Consequently, wireless communication devices provide users with significant mobility, while allowing them to remain “connected” to communication channels and information.
Wireless communication devices communicate with one or more other wireless communication devices or wireless access points to send and receive data. Typically, a first wireless communication device generates and transmits a radio frequency modulated with encoded information. This radio frequency is transmitted into a wireless environment and is received by a second wireless communication device. The second wireless communication device demodulates and decodes the received signal to obtain the information. The second wireless communication device may then respond in a similar manner. The wireless communication devices can communicate with each other or with access points using any well-known modulation scheme, including amplitude modulation (AM), frequency modulation (FM), quadrature amplitude modulation (QAM), phase shift keying (PSK), quadrature phase shift keying (QPSK), and/or orthogonal frequency-division multiplexing, as well as any other communication scheme that is now, or will be, known.
For most modulation schemes, devices employ a technique known as automatic gain control (AGC) in order to normalize the power/strength of all received signals to a particular level. In other words, signals received from a wireless communication environment will have varying levels of power due to channel conditions, such as noise, distance, Doppler Effect, interference, etc. Thus, simply demodulating and outputting the received signals will produce audible volume fluctuations, or other signal distortions, and can result in processing errors and/or low signal-to-quantization noise ratio (SQNR). Thus, AGC is used to reduce high-power signals and/or increase low-power signals to be within a particular range.
Typical AGC adjusts gain by determining a symbol in a received signal with a highest energy and adjusting the gain to bring the symbol within a certain dynamic range. Although this method is generally able to track variations in received power due to varying channel conditions, many other unpredictable factors also affect the tracking, for which typical AGC is unable to compensate.
As another example, in an OFDM communication system, the AGC sets the gain for a future frame based on a most-energetic symbol within a current frame. However, the AGC does not compensate for the frame loading of consecutive OFDM sub-frames, which may cause over and/or under-compensations. Frame loading refers to how many sub-carriers within an OFDM sub-frame are allocated and the power of each of those sub-carriers. When the AGC receives a very heavy-loaded frame (meaning that most sub-carriers are loaded and/or with high power), the AGC will back off gain to compensate. However, since the AGC does not know the frame loading it backs off assuming the worst case scenario of no loading. Often, however, the following frame is not as highly-loaded. Thus, the gain has been overcompensated for the following frame, which may result in processing errors or poor signal outputs.
Thus, there is a need for a wireless communication device that can effectively analyze received signals and adjust signal gain, while accounting for additional data variations that may appear to be channel variations to an AGC, such as frame loading. Further aspects and advantages of the invention will become apparent from the detailed description that follows.
The invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.